Middle Distillate Products Research Articles

Co-processing bio-liquids with vacuum gasoil through hydrocracking

Hydrocracking converts heavy feeds mainly into middle distillate products. Co-processing these bio-feeds with vacuum gas oil is a possible production route for biofuels. Stabilized bio-liquid from fast pyrolysis and hydrothermal liquefaction bio-crude were mixed with vacuum gas oil (10–20 wt%) and hydrocracked over a bifunctional catalyst. The impact of the bio-liquids on conversion and middle distillate selectivity were investigated. The liquid products were analyzed by several methods such as 2-dimensional gas chromatography coupled with simulated distillation to obtain quantitative distribution of monoaromatics, polyaromatics and saturated hydrocarbons. A quantification study of different types of carbons was performed by 13C NMR and showed the evolution of products. The nature of bio-liquid impacts slightly on the conversion and gas production but not on the selectivity of middle distillates and naphtha. This is explained by a decoupled hydrodeoxygenation and hydrocracking process. This also resulted in a high hydrodesulfurization conversion.

Hierarchical ZSM-5 Supported CoMn Catalyst for the Production of Middle Distillate from Syngas

Bifunctional catalysts using hierarchical ZSM-5 zeolite as a support have received more attention for their specific characteristic, which is in favor of producing middle distillate hydrocarbons in Fischer–Tropsch synthesis. The hierarchical structure together with the Bronsted acidity of ZSM-5 zeolites result in the secondary reaction for hydrocracking or isomerization of heavy hydrocarbons. Herein, hierarchical ZSM-5 zeolites with different acidities and mesopore volumes are synthesized by treating zeolites with TPAOH solution. The hierarchical zeolite supported CoMn catalysts are prepared by impregnation method, and all the catalysts are characterized by XRD, BET, XPS, CO/NH₃-TPD, and Py-IR. The results show that the 0.5 M TPAOH solution treated ZSM-5 (Z5-0.5M) possesses the largest mesopore volume and a proper Bronsted acidity. In addition, the Z5-0.5M supported CoMn catalyst exhibits a selectivity of jet fuel range (C₈–C₁₆) as high as 50%, which is much higher than the maximum of 41% predicted by the Anderson–Schulz–Flory model. Moreover, the effect of cobalt loading indicates that the increased cobalt loading leads to the enhancement of CO conversion and the upshift to heavier hydrocarbons.

Various Ways for Increasing Production of Middle Distillate

Currently, refiners are experiencing a big challenge due to the slow economic growth, over diesel production and decreased demand of it. Refineries are searching for technologies that could reduce diesel output, particularly the inferior light cycle oil (LCO) fraction. Here in, this article mainly we will describes the industrialized technologies for LCO processing such as LCO upgrading, LCO blending into available plants such as fluid catalytic cracking (FCC), and hydro-refining/treating unit, LCO moderate hydrocracking, and LCO to some aromatic rich stream and also with gasoline with the integration of selective hydro-refining and resulting optimized FCC unit. It is analyzed that the LCO moderate hydrocracking can provide more gasoline at the expense of high H2 consumption, while LCO to aromatics and gasoline (LTAG) technology needs more steps for clean fuel production and retrofitting of FCC plant. Based on the analyses of current technologies, it is suggested that implementation of such technologies should consider the configuration of refineries, as well as the benefit of end users.

Fischer–Tropsch Synthesis Bifunctional Catalysts: Cobalt Supported on 3D Mesoporous Cellular Silica Foams Assembled by Using ZSM‐5 Seeds

AbstractMesoporous cellular silica foams (MCF) have 3D pore networks in which large spherical cell pores interconnect with small window pores. This novel characteristic provides an open pore structure that favors the accessibility of reactants and mass transfer in reactions. In this work, MCF was functionalized by assembling ZSM‐5 seeds to improve the acidity and the ZSM seed was found to disperse in the MCF structure homogeneously (MCF‐Z). The obtained MCF‐Z materials showed high surface acidity and were then used as supports for cobalt Fischer–Tropsch synthesis (FTS) bifunctional catalysts (20 wt % Co). Compared with Co/MCF catalyst, the Co/MCF‐Z catalysts showed higher CO conversion and improved durability in FTS at 260 °C and 1.0 MPa. Moreover, on increasing the amount of ZSM‐5 seed, the activity of Co/MCF‐Z catalysts gradually increased and then decreased. Co/MCF‐Z catalyst assembled with the highest amount of ZSM‐5 seed (Al/Si=1.5 %, molar ratio) exhibited the lowest deactivation rate, which was owing to the superior stability of the MCF‐Z support and an increased interaction between cobalt and MCF‐Z. The Co/MCF‐Z bifunctional catalyst showed higher iso‐paraffin/n‐paraffin ratios, higher olefin/paraffin ratios as well as lower C2–C4 alcohol selectivity in comparison to Co/MCF catalyst. For the Co/MCF‐Z catalyst, the decrease in space velocity led to hydrocarbon selectivity shifting toward middle distillate products.

Influence of a Zeolite-Based Cascade Layer on Fischer–Tropsch Fuels Production over Silicon Carbide Supported Cobalt Catalyst

In this work, selective production of middle distillate from synthesis gas was conducted over a cascade catalytic system in a single unit. Co/β-SiC was chosen as an efficient Fischer–Tropsch synthesis (FTS) catalyst (first layer) while proton-type H-ZSM-5 and H-βeta zeolites (second layer) were tested for the subsequent hydroprocessing to produce middle distillate from waxes. Moreover, in order to compare, a prior FTS reference experiment was performed. Catalytic materials were characterized by means of Atomic Absorption, Thermogravimetric analysis, X-Ray diffraction, N2 adsorption–desorption, Temperature-Programmed Reduction and Temperature-Programmed Desorption. From catalytic results, a distinguishable enhancement of commercial fuels products was observed under the proposed cascade operation compared to the stand-alone configuration or physical mixture. Regardless the zeolite type, FTS over Co/β-SiC with subsequent upgrading was demonstrated to result in the complete elimination of waxes, solving the main weakness of a conventional fixed-bed reactor. Moreover, apart from a selective production of gasoline, the proposed concept provided a significant enhancement of both kerosene and diesel yields, particularly when zeolite H-βeta is incorporated to the cascade system due to its mild acidity and larger pore size.

Hydrocracking of Maya crude oil in a slurry-phase batch reactor. II. Effect of catalyst load

The effect of the catalyst load in slurry hydrocracking of heavy Maya crude oil was investigated at mild conditions (390°C and 1400 H2 psi). The catalyst load and operating time were varied in the intervals 0–1000ppm Mo and 0–11h respectively. The results allowed to establish the transformation routes of the different fractions under thermal or catalytic conditions. Under thermal conditions, the contributors to gas formation were found to be: Asphaltenes≫resins>vacuum gas–oil and the use of catalyst inhibited the contributions of resins and vacuum gas–oil. It was found that catalytic slurry hydrocracking evolves in two general reaction stages: the first, dominated by the catalyst-induced reactions, from zero to 50% VR conversion, and the second, above 50% VR conversion, dominated by thermal reactions leading to high production of coke. During the first stage the naturally occurring asphaltenes of Maya crude were effectively transformed to liquid fractions and the formation of coke and new asphaltene-like components were catalytically inhibited. Moreover, the production of middle distillates was enhanced. The second reaction stage in catalytic hydrocracking approaches thermal behavior likely because part of the catalyst is lost when the crude mixture above 50% VR conversion departs from physical equilibrium and forms asphaltenic aggregates that precipitate entrapping some catalyst. During the second reaction stage, middle distillates are transformed to light ends, which are end products because no declination was observed in its production. The use of catalyst improves API gravity and viscosity of the liquid product. In all cases the API gravity increased with naphtha production. The hydrodesulfurization results indicate that most of the eliminated sulfur was of asphaltenic nature, presumably associated to the aliphatic lateral chains of asphaltenes. A qualitative estimation of the importance of the different reaction routes is proposed on the basis of the results of this work.

Catalytic degradation of the mixed polyethylene and polypropylene into middle distillate products

Mixture of polymers (HDPE/LDPE/PP) was pyrolyzed over a silico-alumina catalyst using a laboratory semi batch reactor operating isothermally at ambient pressure. The experiments discussed in this work show that the use of catalyst provides proper selectivity in the liquid product distributions and improves the yield of light hydrocarbon productions. The liquid samples were analyzed using GC/FID to find out their composition. The liquid collected at optimum condition (420 °C, 40 cat/pol ratio) was distilled at different temperatures to discretize light and heavy fractions. Octane number, color, Reid vapor pressure, specific gravity, and density are further analyses which done to determine extra physicochemical properties of the liquids at optimum reaction condition. Also, results compared with the physical properties of commercial gasoline which imply that the liquid somewhat matches with standard gasoline. By using Arrhenius’s law, a kinetic model at optimum reaction conditions has been developed and activation energy determined. The reaction follows the first-order kinetic rate relationships. This model equation gives a suitable match with experimental results.

Thermochemical biomass to liquid (BTL) process: Bench-scale experimental results and projected process economics of a commercial scale process

In this paper, we examine the technological feasibility and economic viability of producing liquid fuels from biomass via thermo-chemical route. We initially present laboratory scale production results for synthesizing liquid fuels using syngas derived from biomass. The experiments showed that excellent yield of middle distillate products can be obtained from the bio-derived syngas, but it required supplementing the syngas with hydrogen due to low H2/CO ratio. The results from bench-scale liquefaction unit served as the basis for subsequent modeling and simulation of a biomass to liquid production facility which in turn is used for a preliminary economic analysis of a commercial scale facility using this technology.Two different technologies are compared; one using biomass as the sole feedstock (BTL), while the other augmented biomass derived syngas with hydrogen using the reforming process (BGTL). The idea of co-processing was suggested due to (i) hydrogen deficiency in the biomass feedstock, and, (ii) lower cost of natural gas which is rich in hydrogen. The basis for the design was 2000 metric tons of dry biomass fed per day. We did not include CO2 capture and storage in this study. However, when co-processing was employed, there was significant reduction in CO2 emissions and carbon capture from the biomass increased. A conceptual process capable of 100% feedstock carbon capture is also presented. The breakeven cost of oil (BECOP) was estimated to be $124/bbl for the BTL plant versus $95/bbl for a natural gas assisted BGTL plant using current market prices for raw material and capital equipment. With the increased availability, and falling prices of natural gas, augmentation with natural gas can provide a bridge solution in short term for an economical biomass to liquid fuel technology.

1-Butene oligomerization over ZSM-5 zeolite: Part 1 – Effect of reaction conditions

The demand for middle distillates (kerosene and diesel) in comparison to gasoline fractions is increasing constantly, particularly in the majority of European countries. Thus, maximizing the production of middle distillates in the refining process is of immediate interest to refiners. However, the production of liquid fuels, for instances using a catalytic cracker, always generates a significant amount of lighter fractions, in particular of olefinic nature. Thus, the use of oligomerization reactions to convert the lighter olefin cuts into middle distillates to incorporate in the diesel pool is a promising process for the production of clean diesel fractions. In this work, 1-butene oligomerization over H-ZSM-5 zeolite has been investigated in a differential reactor operating at ambient pressure. The effect of the reaction conditions, such as reaction temperature, contact time and partial pressure was studied on the activity, selectivity and stability of the catalyst. The results show that an increase in the reaction temperature and/or partial pressure and in the contact time produces an improved catalyst activity. The data also show that high partial pressure improves the selectivity to C8+. Moreover, when increasing the temperature from 150°C to 200°C the C8+ hydrocarbons selectivity increases, whereas above this temperature it decreases as expected, due to the competition of cracking reactions. Furthermore, a decrease in contact time between the reaction mixture and the acid sites of the catalyst caused the C8+ hydrocarbons fraction in the product to increase. The highest selectivity towards C8+ hydrocarbons (∼86wt.%) was obtained with H-ZSM-5, at 200°C and 50kPa of partial pressure and for the lowest value of contact time analyzed (12.5×10−3h). In this way, the operating conditions must be tuned in order to achieve a significant conversion and selectivity in desired fraction (C8+).

Pd catalyst supported on SiO 2–Al 2O 3 xerogel for hydrocracking of paraffin wax to middle distillate

SiO 2–Al 2O 3 xerogel supports (SA- X) with different SiO 2 contents ( X, wt%) were prepared by a sol–gel method. Pd catalysts supported on SA- X (Pd/SA- X) were then prepared by an impregnation method for use in the production of middle distillate (C 10–C 20) through hydrocracking of paraffin wax. Acidity of Pd/SA- X catalysts determined by NH 3-TPD experiments showed a volcano-shaped trend with respect to SiO 2 content. Acidity of the catalyst played an important role in determining the catalytic performance in the hydrocracking of paraffin wax. Conversion of paraffin wax increased with increasing acidity of the catalyst, while yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. This indicates that optimal acidity of the catalyst was required for maximum production of middle distillate. Among the catalyst tested, Pd/SA-40 catalyst with moderate acidity showed the highest yield for middle distillate. It was also found that high Pd dispersion of Pd/SA- X catalyst led to the enhanced selectivity for middle distillate in the hydrocracking of paraffin wax.

Deactivation behaviors of hybrid Fischer–Tropsch catalysts in the production of middle distillate from synthesis gas in a dual-bed reactor

Production of middle distillate (C10–C20) from synthesis gas (CO + H2) through hydrocracking of wax (>C21+) was carried out in a dual-bed reactor. Fischer–Tropsch catalyst (Co/TiO2) was used in the first-bed reactor to produce wax from synthesis gas, and a mesoporous Pd–alumina composite catalyst (Pd–Al2O3) was used in the second-bed reactor to produce middle distillate through hydrocracking of wax. Both Fischer–Tropsch synthesis function of Co/TiO2 catalyst and hydrocracking function of Pd–Al2O3 catalyst were deactivated during 100 h-hybrid Fischer–Tropsch synthesis reaction. It was revealed that deactivation behaviors of Co/TiO2 and Pd–Al2O3 catalysts were governed by different factors. Wax accumulation and Co sintering were responsible for deactivation of Co/TiO2 catalyst in the Fischer–Tropsch synthesis reaction. Loss of Pd dispersion and Pd surface area of Pd–Al2O3 catalyst was responsible for its decreased catalytic performance in the production of middle distillate through hydrocracking of wax.

Production of middle distillate through hydrocracking of paraffin wax over NiMo/TiO2-SiO2 catalysts

Titania-silica (TS(X), X=19, 26, 55, 70, and 79) supports with different titania content (X, wt%) were prepared by a precipitation method. NiMo/TS(X) catalysts prepared by an incipient wetness method were then applied to the production of middle distillate through hydrocracking of paraffin wax. Successful formation of NiMo/TS(X) (X=19, 26, 55, 70, and 79) catalysts was confirmed by ICP-AES and XRD measurements. NH3-TPD experiments were conducted to measure the acid property of NiMo/TS(X) (X=19, 26, 55, 70, and 79) catalysts. It was revealed that acidity of the catalyst played an important role in determining the catalytic performance in the hydrocracking of paraffin wax. Conversion of paraffin wax increased with increasing acidity of the catalyst, while yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. Among the catalysts tested, NiMo/TS(26) retaining moderate acidity showed the highest yield for middle distillate.

Production of middle distillate through hydrocracking of paraffin wax over Pd/SiO 2–Al 2O 3 catalysts

Pd/SiO 2–Al 2O 3 catalysts (Pd/SA- X) with different SiO 2 contents ( X, wt%) were prepared for use in the production of middle distillate (C 10–C 20) through hydrocracking of paraffin wax. The effect of SiO 2 content of Pd/SA- X catalysts on their physicochemical properties and catalytic performance in the hydrocracking of paraffin wax was investigated. High surface area and well-developed mesopores of Pd/SA- X catalysts improved the dispersion of Pd species on the SiO 2–Al 2O 3 support. Acidity of Pd/SA- X catalysts determined by NH 3-TPD experiments showed a volcano-shaped trend with respect to SiO 2 content. Conversion of paraffin wax increased with increasing acidity of the catalyst, while selectivity for middle distillate decreased with increasing acidity of the catalyst. Yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. This indicates that acidity of Pd/SA- X catalysts played an important role in determining the catalytic performance in the hydrocraking of paraffin wax. Among the catalyst tested, Pd/SA-69 with moderate acidity showed the highest yield for middle distillate.

Production of middle distillate through hydrocracking of paraffin wax over Pd0.15Cs x H2.7−x PW12O40 catalysts: Effect of cesium content and surface acidity

Palladium-exchanged heteropolyacid (Pd0.15CsxH2.7−xPW12O40) catalysts were prepared by an ion-exchange method with a variation of cesium content (x=2.0, 2.2, 2.5, and 2.7) for use in the production of middle distillate through hydrocracking of paraffin wax. Surface acidity of Pd0.15CsxH2.7−xPW12O40 catalysts determined by NH3-TPD experiments showed a volcano-shaped trend with respect to cesium content. Surface acidity of the catalysts played an important role in determining the catalytic performance in the hydrocracking of paraffin wax. Conversion of paraffin wax increased with increasing surface acidity of the catalyst, while yield for middle distillate showed a volcano-shaped curve with respect to surface acidity of the catalyst. Among the catalysts tested, Pd0.15Cs2.7PW12O40 catalyst with moderate surface acidity showed the best catalytic performance.

Production of Middle Distillate Through Hydrocracking of Paraffin Wax Over NiMo/SiO2-Al2O3 Catalysts: Effect of Solvent in the Preparation of SiO2-Al2O3 by a Sol–Gel Method

SiO2-Al2O3 supports were prepared by a sol–gel method in the presence of distilled water and ethanol, respectively (SiO2-Al2O3 supports were donated as H-SA and E-SA, respectively). NiMo/SiO2-Al2O3 catalysts (NiMo/H-SA and NiMo/E-SA) were then prepared by an impregnation method for use in the production of middle distillate (C10–C20) through hydrocracking of paraffin wax. The effect of solvent in the preparation of SiO2-Al2O3 support on the catalytic performance of NiMo/SiO2-Al2O3 catalyst was investigated. NiMo/H-SA catalyst showed a higher conversion of wax and a higher selectivity for middle distillate than NiMo/E-SA catalyst. The identity of solvent strongly affected the physical properties of H-SA and E-SA supports. High surface area of H-SA enhanced the dispersion of impregnated metal species, resulting in the increase of active sites of NiMo/H-SA catalyst. Large pore volume and large pore diameter of NiMo/H-SA catalyst played an important role in enhancing internal mass transfer during the reaction. Large acidity of NiMo/H-SA catalyst compared to NiMo/E-SA catalyst was responsible for high conversion of wax over NiMo/H-SA catalyst. The enhanced selectivity for middle distillate over NiMo/H-SA catalyst was attributed to abundant active sites for hydrogenation reaction.

Middle distillates from hydrocracking of FT waxes: Composition, characteristics and emission properties

A light cobalt catalyzed Fischer–Tropsch (FT) wax was subjected to hydrocracking in the range of temperature 319–351 °C and hydrogen pressure between 3.5 and 6.0 MPa. The catalyst used was platinum on amorphous silica–alumina. Hydrocracking reaction led to an increase of middle distillate yield up to 85% with a contemporary increase of iso-paraffins concentration which resulted in a remarkable improvement of cold flow properties of the products. The freezing point of C 10–C 14 fraction passed from −23 to −45 °C while the pour point of C 15–C 22 fraction decreased from 13 to −23 °C. The latter fraction displayed high cetane numbers ranging between 75 and 80. Changes in carbon distribution and molecular structure of products during hydrocracking have been rationalized in the light of the accepted hydrocracking mechanism where n-paraffins undergo to consecutive isomerization reactions leading to isomers with progressively higher branching degree and concomitant cracking reaction. Experimental evidences support the view that apparent reactivity of n-paraffins is chain length dependent, increasing with the molecular weight. Detailed characterization by NMR and GC showed that branching groups abundance in the middle distillate products was the following: methyl ≫ ethyl > propyl. Emission tests carried out with FT diesel and commercial ultra low sulfur diesel showed that FT diesel has excellent combustion properties and leads to a reduction of emissions.

Production of Middle Distillate from Synthesis Gas in a Dual-bed Reactor Through Hydrocracking of Wax Over Mesoporous Pd-Al2O3 Composite Catalyst

Production of middle distillate (C10–C20) from synthesis gas (CO + H2) through hydrocracking of wax (>C21+) was carried out in a dual-bed reactor. Co/TiO2 catalyst was used in the first-bed reactor to produce wax from synthesis gas, and a mesoporous Pd-alumina composite catalyst (Pd-Al2O3) was used in the second-bed reactor to produce middle distillate through hydrocracking of wax. For comparison, a Pd catalyst supported on mesoporous alumina (Pd/Al2O3) was also examined as a second-bed catalyst. The catalytic performance of Pd-Al2O3 and Pd/Al2O3 for hydrocracking of wax to middle distillate was tested and compared. It was revealed that selectivity for middle distillate in the dual-bed reactor was much higher than that in the first-bed reactor, indicating that both Pd-Al2O3 and Pd/Al2O3 catalysts in the second-bed reactor served as an efficient catalyst for hydrocracking of wax to middle distillate. Furthermore, Pd-Al2O3 catalyst showed a higher selectivity for middle distillate than Pd/Al2O3. The enhanced catalytic performance of Pd-Al2O3 for hydrocracking of wax to middle distillate was due to high Pd dispersion and high Pd surface area. Large medium acidity of Pd-Al2O3 catalyst was also responsible for its high catalytic performance in the hydrocracking of wax to middle distillate.

Production of Middle Distillate Through Hydrocracking of Paraffin Wax over NiMo/SiO2–Al2O3 Catalysts: Effect of SiO2–Al2O3 Composition on Acid Property and Catalytic Performance of NiMo/SiO2–Al2O3 Catalysts

SiO2–Al2O3 supports with different composition were prepared by a precipitation method in order to control the acid property of SiO2–Al2O3 supports. NiMo/SiO2–Al2O3 catalysts were then prepared by an impregnation method and sulfided for use in the production of middle distillate through hydrocracking of paraffin wax. It was revealed that MoS2 phase was dominantly formed in the NiMo/SiO2–Al2O3 catalysts, while Ni–Mo–S phase was not detected due to its fine dispersion. Acidity of NiMo/SiO2–Al2O3 catalysts measured by NH3–TPD experiments showed a volcano-shaped curve with respect to SiO2 content. Acidity of the catalysts played an important role in determining the catalytic performance in the hydrocracking of paraffin wax. Conversion of paraffin wax was monotonically increased with increasing acidity of the catalyst, while yield for middle distillate showed a volcano-shaped curve with respect to acidity of the catalyst. Thus, optimal acidity of NiMo/SiO2–Al2O3 catalysts was required for the maximum production of middle distillate through hydrocracking of paraffin wax.

Effect of calcination temperature of alumina supports on the wax hydrocracking performance of Pd-loaded mesoporous alumina xerogel catalysts for the production of middle distillate

Abstract Selective production of middle distillate (C10–C20) from synthesis gas (CO + H2) through wax hydrocracking was carried out in a dual-bed reactor. Co/TiO2 catalyst was used in the first-bed reactor to produce wax (C21+) from synthesis gas, and Pd-loaded mesoporous alumina xerogel (denoted as Pd/XA) catalysts were used in the second-bed reactor to produce middle distillate through wax hydrocracking. The effect of calcination temperature of mesoporous alumina xerogel supports on the wax hydrocracking performance of Pd/XA catalysts was investigated. The increment of middle distillate selectivity increased with increasing medium acidity of Pd/XA catalyst. Among the Pd/XA catalysts, the Pd catalyst loaded on mesoporous alumina xerogel support calcined at 800 °C retained the highest medium acidity, and at the same time, showed the best catalytic performance in the hydrocracking of wax.

Production of middle distillate in a dual-bed reactor from synthesis gas through wax cracking: Effect of acid property of Pd-loaded solid acid catalysts on the wax conversion and middle distillate selectivity

Selective production of middle distillate (C10–C20) from synthesis gas (CO+H2) was carried out in a dual-bed reactor. Co-based catalysts were used in the first-bed reactor to produce wax (C21+) from synthesis gas, and Pd-loaded solid acid catalysts were used in the second-bed reactor to produce middle distillate from wax through hydrocracking. Co/TiO2 catalyst in the first-bed reactor produced more than 35wt% middle distillate and more than 20wt% wax. These products served as a suitable feed for the production of middle distillate through hydrocracking in the second-bed reactor. Pd-loaded solid acid catalysts used in the second-bed reactor retained three types of acid sites (weak-, medium-, and strong-acid sites). Correlations between medium acidity and catalytic activity of Pd-loaded solid acid catalyst revealed that wax conversion and increment of middle distillate selectivity in the second-bed reactor were increased with increasing medium acidity of the catalyst. Total acidity of Pd-loaded solid acid catalyst was increased with increasing medium acidity of the catalyst. Thus, the medium acidity (total acidity) of Pd-loaded solid acid catalyst served as a crucial factor in hydrocracking of wax. Among the second-bed catalysts, the Pd/mesoporous alumina (Pd/MA) catalyst with the highest medium acidity (total acidity) showed the best catalytic performance (ca. 83% wax conversion and ca. 15wt% increment of middle distillate selectivity).